Regular parabolic trough solar collectors are typically built with rugged structural members to provide rigidity so that when one part of the trough is rotated by a sun-tracking mechanism, the whole trough rotates together. The parabolic reflectors are typically glass or highly polished metal. U.S. Pat. Nos. 4,114,694 and 5,058,565 show trough structures that can be rotated by external means, but the troughs have to be rotationally rigid.
The rigid structures of these troughs are expensive, and the reflecting surfaces are expensive.
The tubes that carry the cooling fluid are typically located somewhat above the parabolic reflector. These designs are typically quite sensitive to the accuracy of the sun-tracking system. That is, if the troughs are not pointed fairly accurately toward the sun, the reflected rays tend to miss the target (the pipe carrying the cooling fluid). U.S. patents such as U.S. Pat. Nos. 3,923,381 and 6,676,263 overcome this problem by having a fairly narrow channel for concentrating the sunrays, and the fluid pipe is located deep within the cavity. These troughs also require rigid and expensive structures to maintain the geometry of the troughs.